Method and assembly for determining the temperature of a test sensor

ABSTRACT

An assembly determines an analyte concentration in a sample of body fluid. The assembly includes a test sensor having a fluid-receiving area for receiving a sample of body fluid, where the fluid-receiving area contains a reagent that produces a measurable reaction with an analyte in the sample. The assembly also includes a meter having a port or opening configured to receive the test sensor; a measurement system configured to determine a measurement of the reaction between the reagent and the analyte; and a temperature-measuring system configured to determine a measurement of the test-sensor temperature when the test sensor is received into the opening. The meter determines a concentration of the analyte in the sample according to the measurement of the reaction and the measurement of the test-sensor temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/105,806, having a filing date of Dec. 18, 2008, the contents of whichare incorporated entirely herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a method and assembly fordetermining an analyte concentration in a sample of body fluid collectedon a test sensor. More specifically, the present invention generallyrelates to a method and assembly for measuring the temperature of thetest sensor to determine the temperature of a reagent reacting with theanalyte and to achieve an accurate determination of the analyteconcentration based on the reaction with the reagent.

BACKGROUND OF THE INVENTION

The quantitative determination of analytes in body fluids is of greatimportance in the diagnoses and maintenance of certain physiologicalabnormalities. For example, lactate, cholesterol and bilirubin aremonitored in certain individuals. In particular, it is important thatindividuals with diabetes frequently check the glucose level in theirbody fluids to regulate the glucose intake in their diets. The resultsof such tests can be used to determine what, if any, insulin or othermedication needs to be administered. In one type of blood-glucosetesting system, test sensors are used to test a sample of blood.

A test sensor contains biosensing or reagent material that reacts with,for example, blood glucose. For example, the testing end of the sensormay be adapted to be placed into contact with the fluid being tested(e.g., blood) that has accumulated on a person's finger after the fingerhas been pricked. The fluid may be drawn into a capillary channel thatextends in the sensor from the testing end to the reagent material bycapillary action so that a sufficient amount of fluid to be tested isdrawn into the sensor. The tests are typically performed using a meterthat receives the test sensor into a test-sensor opening and appliesoptical or electrochemical testing methods.

The accuracy of such testing methods however may be affected by thetemperature of the test sensor. For example, the result of the chemicalreaction between blood glucose and a reagent on a test sensor may varyat different temperatures. To achieve an accurate reading, the actualmeasurement is corrected based on the actual sensor temperature, takenright before the reaction begins. The conventional way to measure thetest sensor temperature involves reading a resistive value from athermistor placed near the test-sensor opening. The thermistorresistance recalculates the chemical reaction result. This correctionmethod is based on an assumption that a sensor temperature is the sameas the thermistor temperature placed near the test-sensor opening. Inreality, however, the thermistor, which is typically located on aprinted circuit board, actually provides the temperature of the meter.Because the temperature of the meter can be very different from the testsensor temperature, the analyte measurement may be inaccurate.

As a result, it would be desirable to have a method and assembly thataccurately measures and accounts for the temperature of the test sensorfor achieving an accurate analyte measurement.

SUMMARY OF THE INVENTION

Reagents that are used to measure analyte concentration in a sample ofbody fluid may be sensitive to changes in temperature. In other words,the magnitude of the reaction between the reagent and the analyte maydepend on the temperature of the reagent. As a result, any calculationof the analyte concentration in the sample based on the reaction mayvary with the temperature of the reagent. Accordingly, to achieve a moreaccurate measurement of the analyte concentration, embodiments of thepresent invention also determine the temperature of the reagent. Thetemperature of the reagent is used by an algorithm which determines theanalyte concentration. Embodiments may determine the reagent temperatureby measuring the temperature of a test sensor that holds the reagent ina fluid-receiving area for reaction with a collected sample. Inparticular, these embodiments measure the test-sensor temperature whilethe area of the test sensor being measured is in equilibrium with thereagent temperature.

One embodiment provides an assembly for determining an analyteconcentration in a sample of body fluid. The assembly includes a testsensor having a fluid-receiving area for receiving a sample of bodyfluid, where the fluid-receiving area contains a reagent that produces ameasurable reaction with an analyte in the sample. The test sensor has agrating disposed along a surface of the test sensor, the gratingincluding a series of parallel linear structures equally separated by adistance that changes in response to temperature. The assembly alsoincludes a meter having a port or opening configured to receive the testsensor; a measurement system configured to determine a measurement ofthe reaction between the reagent and the analyte; and atemperature-measuring system configured to determine a measurement ofthe test-sensor temperature when the test sensor is received into theopening. The temperature-measuring system includes a light source and alight detector, the light source being configured to direct incidentlight to the grating, and the detector being configured to receive, fromthe grating, diffracted light that changes according to changes in thedistance separating the linear structures of the grating. Thetemperature-measuring system determines the measurement of thetest-sensor temperature according to the diffracted light. The meterdetermines a concentration of the analyte in the sample according to themeasurement of the reaction and the measurement of the test-sensortemperature.

In one example, the light source includes a laser of a fixed wavelengthdirected to the grating. The detector receives the diffracted light fromthe grating according to an angle. The angle indicates the distanceseparating the linear structures of the grating, and thetemperature-measuring system determines the measurement of thetest-sensor temperature according to the angle.

In another example, the light source generates white light and directsthe white light to the grating. The detector receives the diffractedlight from the grating. The diffracted light includes red, green, andblue (RGB) components. The RGB components in the diffracted lightindicates the distance separating the linear structures of the grating,and the temperature-measuring system determines the measurement of thetest-sensor temperature according to the angle.

Another embodiment provides an assembly for determining an analyteconcentration in a sample of body fluid. The assembly includes a testsensor having a fluid-receiving area for receiving a sample of bodyfluid, where the fluid-receiving area contains a reagent that produces ameasurable reaction with an analyte in the sample. The test sensor has apolarizing material disposed along a surface of the test sensor. Thepolarizing material causes a degree of polarization of light reflectedfrom the polarizing material. The polarizing material has a structurethat changes in response to temperature and changes the degree ofpolarization. The assembly also includes a meter having a port oropening configured to receive the test sensor; a measurement systemconfigured to determine a measurement of the reaction between thereagent and the analyte; and a temperature-measuring system configuredto determine a measurement of the test-sensor temperature when the testsensor is received into the opening. The temperature-measuring systemincludes a light source and a light detector, the light source beingconfigured to direct incident light to the polarizing material, and thedetector being configured to receive, from the polarizing material, anamount of reflected light that changes according to the degree ofpolarization. The temperature-measuring system determining themeasurement of the test-sensor temperature according to the amount ofreflected light received by the detector. The meter determines aconcentration of the analyte in the sample according to the measurementof the reaction and the measurement of the test-sensor temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general diagnostic system, including a test sensorand a meter, according to an embodiment of the present invention.

FIG. 2 illustrates the embodiment of FIG. 1 with the test sensorinserted into the meter.

FIG. 3A illustrates a partial plan view of a meter according to anembodiment of the present invention.

FIG. 3B illustrates an enlarged transparent partial view of the meter ofFIG. 3A.

FIG. 3C illustrates an internal side view of the meter of FIG. 3A.

FIG. 3D illustrates yet another internal view of the meter of FIG. 3A.

FIG. 3E illustrates yet another internal view of the meter of FIG. 3A.

FIG. 3F illustrates an example processing system for the meter of FIG.3A.

FIG. 4A illustrates a thermopile sensor and a thermistor that may beused by an embodiment of the present invention.

FIG. 4B illustrates a bottom view of the thermopile sensor and thethermistor of FIG. 4A.

FIG. 5 illustrates a configuration for an optical-sensing system thatmay be used by an embodiment of the present invention.

FIG. 6 illustrates a view of a test sensor employing a thermochromicliquid crystals according to an embodiment of the present invention.

FIG. 7 illustrates molecular changes of the thermochromic liquid crystalwith temperature.

FIG. 8 illustrates the range of the color of the thermochromic liquidcrystal depending on temperature.

FIG. 9 illustrates a graph of temperature vs. time and optical intensity(RGB) vs. time from an example experimental setup.

FIG. 10 illustrates a graph of temperature vs. color intensity (RGB)converted from the data of the graph of FIG. 9.

FIG. 11A illustrates a subroutine for optical processing to convert RGBdata into temperature data.

FIG. 11B illustrates a general algorithm to process optical data toconvert RGB data into temperature data.

FIG. 12 illustrates a graph of temperature vs. time and opticalintensity (RGB) vs. time for 20° C. to 40° C. temperature tests.

FIG. 13 illustrates a graph of temperature vs. color intensity (RGB)converted from the data of the graph of FIG. 12.

FIG. 14 illustrates TCLC-based temperature and thermocouple datacorresponding to the data of FIGS. 12 and 13.

FIG. 15 illustrates a “sliced-pie TCLC configuration” for measuringtemperatures with an array of TCLC materials according to aspects of thepresent invention.

FIG. 16 illustrates a configuration for another optical-sensing systemthat may be used by an embodiment of the present invention.

FIG. 17 illustrates a configuration for a further optical-sensing systemthat may be used by an embodiment of the present invention.

FIG. 18 illustrates a configuration for yet another optical-sensingsystem that may be used by an embodiment of the present invention.

FIG. 19 illustrates a system for calibrating a device, such as a CGMsensor, with a controller having a temperature-measuring systemaccording to aspects of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments are shown by way of example inthe drawings and are described in detail herein. It should beunderstood, however, that the invention is not intended to be limited tothe particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Aspects of the present invention provide methods and assemblies formeasuring the temperature of a reagent on a test sensor used to collecta sample of body fluid. The reagent reacts with an analyte in the sampleof body fluid and the level of reaction may be measured to determine theconcentration of analyte in the sample. The level of reaction may beaffected by changes in temperature of the reagent. By measuring thetemperature of the reagent, aspects of the present invention may accountfor the reagent's sensitivity to temperature and thus obtain a moreaccurate calculation of the concentration of analyte in the sample.

Referring to FIG. 1, a diagnostic system 10 with a test sensor 100 and ameter 200 is illustrated. The test sensor 100 is configured to receive afluid sample and is analyzed using the meter 200. Analytes that may beanalyzed include glucose, lipid profiles (e.g., cholesterol,triglycerides, LDL and HDL), microalbumin, hemoglobin A_(1C), fructose,lactate, or bilirubin. It is contemplated that other analyteconcentrations may be determined. The analytes may be in, for example, awhole blood sample, a blood serum sample, a blood plasma sample, otherbody fluids like ISF (interstitial fluid) and urine, and non-bodyfluids. As used within this application, the term “concentration” refersto an analyte concentration, activity (e.g., enzymes and electrolytes),titers (e.g., antibodies), or any other measure concentration used tomeasure the desired analyte.

As shown in FIG. 1, the test sensor 100 includes a body 105 having afluid-receiving area 110 for receiving a sample of body fluid. Forexample, a user may employ a lancet or a lancing device to pierce afinger or other area of the body to produce the blood sample at the skinsurface. The user may then collect this blood sample by placing anopening 107 of the test sensor 100 into contact with the sample. Theblood sample may flow from the opening 107 to the fluid-receiving area110 via a capillary channel 108, as generally depicted in the embodimentof FIG. 1. The fluid-receiving area 110 may contain a reagent 115 whichreacts with the sample to indicate the concentration of an analyte inthe sample. The test sensor 100 also has a meter-contact area 112 whichis received by the meter 200 as described in detail further below.

The test sensor 100 may be an electrochemical test sensor. Anelectrochemical test sensor typically includes a plurality of electrodesand a fluid-receiving area that contains an enzyme. The fluid-receivingarea includes a reagent for converting an analyte of interest (e.g.,glucose) in a fluid sample (e.g., blood) into a chemical species that iselectrochemically measurable, in terms of the electrical current itproduces, by the components of the electrode pattern. The reagenttypically contains an enzyme such as, for example, glucose oxidase,which reacts with the analyte and with an electron acceptor such as aferricyanide salt to produce an electrochemically measurable speciesthat can be detected by the electrodes. It is contemplated that otherenzymes may be used to react with glucose such as glucose dehydrogenase.In general, the enzyme is selected to react with the desired analyte oranalytes to be tested so as to assist in determining an analyteconcentration of a fluid sample. If the concentration of another analyteis to be determined, an appropriate enzyme is selected to react with theanalyte. Examples of electrochemical test sensors, including theiroperation, may be found in, for example, U.S. Pat. No. 6,531,040assigned to Bayer Corporation. It is contemplated, however, that otherelectrochemical test sensors may be employed.

Alternatively, the test sensor 100 may be an optical test sensor.Optical test sensor systems may use techniques such as, for example,transmission spectroscopy, diffuse reflectance, or fluorescencespectroscopy for measuring the analyte concentration. An indicatorreagent system and an analyte in a sample of body fluid are reacted toproduce a chromatic reaction, as the reaction between the reagent andanalyte causes the sample to change color. The degree of color change isindicative of the analyte concentration in the body fluid. The colorchange of the sample is evaluated to measure the absorbance level of thetransmitted light. Transmission spectroscopy is described in, forexample, U.S. Pat. No. 5,866,349. Diffuse reflectance and fluorescencespectroscopy are described in, for example, U.S. Pat. Nos. 5,518,689(titled “Diffuse Light Reflectance Read Head”), 5,611,999 (titled“Diffuse Light Reflectance Read Head”), and 5,194,393 (titled “OpticalBiosensor and Method of Use”).

As further illustrated in FIG. 1, the meter 200 includes a body portion205 with a test sensor opening 210, which includes a connector forreceiving and/or holding a test sensor 100. The meter 200 also includesa measurement system 220 for measuring the concentration of analyte forthe sample in fluid-receiving area 110. For example, the measurementsystem 220 may include contacts for the electrodes to detect theelectrochemical reaction for an electrochemical test sensor.Alternatively, the measurement system 220 may include an opticaldetector to detect the chromatic reaction for an optical test sensor. Toprocess information from the measurement system 220 and to generallycontrol the operation of the meter 200, the meter 200 may employ atleast one processing system 230, which may execute programmedinstructions according to a measurement algorithm. Data processed by theprocessing system 230 may be stored in a conventional memory device 235.Furthermore, the meter may have a user interface 240 which includes adisplay 245, which, for example, may be a liquid-crystal display.Pushbuttons, a scroll wheel, touch screens, or any combination thereof,may also be provided as a part of the user interface 240 to allow a userto interact with the meter 200. The display 245 typically showsinformation regarding the testing procedure and/or information inresponse to signals input by the user. The result of the testing mayalso be announced audibly, by, for example, using a speaker.

In general operation, a user removes a test sensor 100 from a package,such as a container, at time t₀. The user then inserts the test sensor100 into the test-sensor opening 210 at time t₁, as shown in FIG. 2.Upon insertion of the test sensor 100 at time t₁, the meter 200 isactivated, i.e. wakes up, to begin a predefined testing procedureaccording to one method. In particular, a signal is sent from thetest-sensor opening 210 to wake up the measurement system 220. Thissignal, for example, may be mechanically or electrically generated. Theuser then places the test sensor 100 at time t_(s) into contact with asample of body fluid, which is received into the fluid-receiving area110. The sample then reacts with the reagent 115, and the measurementsystem 220 measures the level of reaction. The processing system 230receives information on the reaction, e.g. in the form of a electricalsignal, and determines the amount of analyte concentration in the sampleaccording to the measurement algorithm. The results of this measurementmay then be recorded in memory device 235 and/or displayed to the uservia the display 245.

Diagnostic systems, such as blood-glucose testing systems, typicallycalculate the actual glucose value based on a measured output and theknown reactivity of the reagent-sensing element (e.g., test sensor 100)used to perform the test. Calibration information is generally used tocompensate for different characteristics of test sensors, which willvary on a batch-to-batch basis. The calibration information may be, forexample, the lot specific reagent calibration information for the testsensor. The calibration information may be in the form of a calibrationcode. Selected information associated with the test sensor (which mayvary on a batch-to-batch basis) is tested to determine the calibrationinformation to be used in association with the meter. The reactivity orlot-calibration information of the test sensor may be provided on acalibration circuit that is associated with the sensor package or thetest sensor. This calibration circuit may be inserted by the end user.In other cases, the calibration is automatically done using anauto-calibration circuit via a label on the sensor package or the testsensor. In these cases, calibration is transparent to the end user anddoes not require that the end user insert a calibration circuit into themeter or enter coding information. Some embodiments of the presentinvention may provide either a manual- or auto-calibrating diagnosticsystem. In the example shown in FIG. 1, the diagnostic system 10 isauto-calibrating, so the test sensor 100 may include an auto-calibrationinformation area 120, which may include a label, at the meter-contactarea 112.

As discussed previously, the temperature of the reagent on the testsensor 100 may affect the accuracy of the concentration of analytecalculated by the meter 200, as the level of reaction between theanalyte and the reagent 115 may be dependent on the temperature of thereagent 115. As such, some embodiments of the present inventiondetermine a temperature for the reagent 115 and use this calculatedtemperature to produce a more accurate measurement of the analyteconcentration. In particular, the meter 200 has a temperature-measuringsystem 250 and the processing system 230 uses this calculatedtemperature from the temperature-measuring system 250 as a variableinput for a measurement algorithm.

In operation, when a test sensor 100 is inserted at time t₁ into thetest-sensor opening 210 of the meter, the temperature of the test sensor100 is also measured with the temperature-measuring system 250. Althoughthe system 250 may actually measure the temperature of the test sensor100, i.e., the meter-contact area 112, instead of the temperature of thereagent 115, the temperatures of the test sensor 100 and the reagent 115are generally at equilibrium with the ambient temperature when the testsensor 100 is inserted into the test-sensor opening 210 at time t₁. Asshown in FIG. 2, when the test sensor 100 is inserted into thetest-sensor opening 210, the meter-contact area 112 is positioned in thetest-sensor opening 210, but the fluid-receiving area 110 may bepositioned distally from the meter 200. As such, the meter-contact area112 may be heated by sources of heat in the meter 200, such ascomponents receiving power from a power source. However, thefluid-receiving area 110 and the reagent 115 may be sufficiently spacedfrom the sources of heat to remain substantially at ambient temperature.Thus, determining the ambient temperature provides a useful estimate ofthe temperature of the reagent 115, which is used as a factor indetermining analyte concentration. It is noted that for a brief time,the temperature of the fluid-receiving area 110 may increase at timet_(s) when it receives the fluid sample, which may retain some heat fromthe body. It has been determined that for a short time period, e.g.,approximately 0.5 seconds to approximately 5 seconds, after the testsensor 100 has been inserted into the test-sensor opening 210 at timet₁, the ambient temperature can still be determined from themeter-contact area 112 before the temperature of the area 112 increasesdue to heat from the meter 200 or decreases due to cooling from themeter 200. The time period for determining the ambient temperature fromthe meter-contact area 112 may vary from the time that the test sensoris inserted, e.g., approximately 0.5 seconds to approximately 5 seconds,depending on factors, such as the type of meter being used, etc. It isunderstood that the time range provided here, i.e., approximately 0.5seconds to approximately 5 seconds, is provided as an example and thatother time periods may be appropriate. Other such factors are discussedfurther below. Accordingly, some embodiments of the present inventionmay measure the temperature of area 112 at time t₁ when the effects ofheat or cooling from the meter 200 are still at a minimum.

Although some embodiments may measure the temperature of area 112 attime t₁ described above, other embodiments may measure the temperatureat other times. Even if the effects of heat or cooling from the meter200 have already changed the temperature of the area 112 at the time ofmeasurement, the temperature of the area 112 prior to the effects ofheat or cooling may be determined by applying an algorithm to themeasurement. For example, the temperature as a function of time, i.e., atemperature-time curve, may be applied to extrapolate backwards from themeasurement to determine a temperature at time t₁, before the actualmeasurement time.

As shown in FIG. 2 and FIGS. 3A-E, the temperature-measuring system 250is positioned in the test-sensor opening 210 of the meter body 205, suchthat the temperature-measuring system 250 may be positioned in proximityto the test sensor 100 when it is inserted into the test-sensor opening210. In the embodiment illustrated by FIGS. 3A-E, thetemperature-measuring system 250 includes a thermopile sensor 250Adisposed at a position 251 within the test-sensor opening 210, forexample on a printed circuit board 231.

Although some embodiments may include a temperature-measuring system 250disposed at a position 251 within the test-sensor opening 210, atemperature-measuring system 250 may be disposed at other areas to allowtemperature measurement of test sensor 100. For example, thetemperature-measuring system 250 may be positioned on a structure, suchas an arm, that extends outwardly from the meter body 205 to measure anarea of the test sensor 100 that is positioned outside the test-sensoropening 210 when the test sensor 100 is inserted into the test-sensoropening 210. The structure may extend permanently from the meter body205 or may be operated manually or triggered automatically to extend orswing out into an appropriate position for measuring an area of the testsensor 100. Moreover, other embodiments may include more than onestructure disposed anywhere relative to the meter body 205 for measuringmore than one area of the test sensor 100. Temperature measurements frommore than one area may provide a more accurate determination of thetemperature for the reagent 115. For example, unlike the configurationof FIG. 3E, the test sensor 100 may be inserted transversely, ratherthen longitudinally, into a test-sensor opening 210, so that more thanone area along the test sensor 100 may be accessed to obtain temperaturemeasurements.

In general, all materials at temperatures above absolute zerocontinuously emit energy. Infrared radiation is part of theelectromagnetic spectrum and occupies frequencies between visible lightand radio waves. The infrared (IR) part of the spectrum spanswavelengths from about 0.7 micrometers to about 1000 micrometers. Thewave band usually used for temperature measurement is from about 0.7 toabout 20 micrometers. The thermopile sensor 250A measures the actualsensor strip temperature by using blackbody radiation emitted from thetest sensor 100. By knowing the amount of infrared energy emitted by thetest sensor 100 and its emissivity, the actual temperature of the testsensor 100 can be determined. In particular, the thermopile sensor 250Amay generate a voltage proportional to incident infrared radiation.Because the temperature of a surface of the test sensor 250A is relatedto the incident infrared radiation, the temperature of the surface canbe determined from the thermopile sensor 250A.

When the test sensor 100 is received into the test-sensor opening 210,the position 251 of the thermopile sensor 250A is proximate, orsubstantially adjacent, to the test sensor 100. The position 251 ensuresthat the infrared radiation detected by the thermopile sensor 250A comessubstantially from the test sensor 100. In other words, the thermopilesensor 250A may be positioned to minimize the effect of light fromexternal sources, e.g., ambient light, on the readings of the thermopilesensor 250A. While FIG. 3E, for example, show the thermopile sensor 250Abelow the test sensor 100, it is understood that the thermopile sensormay be positioned in other appropriate positions relative to the testsensor.

FIG. 3F illustrates aspects of a processing system 230 that may beemployed for implementing the thermopile sensor 250A in the meter 200.First, an output electrical signal from the thermopile sensor 250A isreceived by an analog amplifier 230A. The amplified analog signal fromthe analog amplifier 230A is passed to an analog-to-digital converter230C via an analog filter 230B. The analog-to-digital converter 230Cdigitizes the amplified analog signal, which may subsequently befiltered by a digital filter 230D. The digital signal is thentransmitted to a microcontroller 230E. The microcontroller 230Ecalculates the temperature of the test sensor 100 based on the magnitudeof the output electrical signal from the thermopile sensor 250A and thecalculated temperature is employed to correct the initial blood glucosemeasurement from the measurement system 220. For some embodiments, it iscontemplated that the analog filter 230B, the analog-to-digitalconverter 230C, and the digital filter 230D may be incorporated into themicrocontroller 230E. In some embodiments, the analog filter 230B andthe analog-to-digital converter 230C may be integrated into anapplication-specific integrated circuit (ASIC). In further embodiments,a memory, such as an EEPROM, may be employed to store calibration dataand the like. Moreover, it is further contemplated that in someembodiments the analog filter 230B and the digital filter 230D may beoptional. It is also noted that although the thermopile sensor 250A inFIG. 3F is positioned opposite from the electrical contacts 221 thatreceive the test sensor electrodes, other embodiments may position thethermopile sensor to be on the same side of the test sensor.

FIGS. 4A and 4B illustrate a typical thermopile sensor 250A, whichincludes a series of thermal elements hermetically sealed in a metalhousing 255A. In particular, the thermopile sensor 250A may include anoptical filter 257A and an absorbing area 258A. It is contemplated thatthe thermopile sensor 250A may be housed in a variety of TO housings orsurface mount device housings. The time constant for the thermopilesensor 250A is of the order of 100 ms or less, which correspondsoperationally with diagnostic systems 10 which have typical test timesof the order of approximately 5 seconds. In general, the thermopilesensor 250A provides sufficient sensitivity, a small temperaturecoefficient of sensitivity, as well as high reproducibility andreliability.

As illustrated in FIGS. 4A and 4B, the temperature-measuring system 250may optionally include an additional reference temperature sensor 260A,such as a sensor, thermistor, semiconductor temperature sensor, or thelike. This reference temperature resistor, or thermistor, 260A may alsobe included in the housing 255A. As such, the temperature-measuringsystem 250 shown in FIGS. 3A-F can provide the temperature of the testsensor 100 and the reference temperature of the meter body 205 asvariable inputs for the measurement algorithm run by the processingsystem 230. Accordingly, the temperature-measuring system 250 of FIGS.4A and 4B has two pins, e.g. pins 1 and 3, corresponding to thethermopile sensor 250A and two pins, e.g. pins 2 and 4, corresponding tothe thermistor 260A. Thus, the meter 200 measures the voltage across thepins 1 and 3, which indicates the amount of infrared radiationassociated with the temperature of the test sensor 200. In addition, themeter measures the resistance across pins 2 and 4, which indicates thetemperature of the meter body 205. It is contemplated that other typesof contact structures, such as pads, may be employed, and embodimentsare not limited to the use of the pins shown in FIGS. 4A and 4B.

For example, the meter 200 may be equipped with a Heimann HMS Z11-F5.5Ultrasmall Thermopile Sensor (Heimann Sensor GmbH, Dresden, Germany),which provides a Complementary Metal Oxide Semiconductor (CMOS)compatible sensor chip plus a thermistor reference chip. The HMSZ11-F5.5 is 3.55 mm in diameter and 2.4 mm in height. It is contemplatedthat other thermopile sensors may be used, having different dimensions.Advantageously, the compact dimensions of such a thermopile sensorenable the thermopile sensor to be packaged within known meterconfigurations and positioned at the test-sensor opening into which thetest sensor is inserted.

In one study, a meter was configured with a Heimann HMS B21 ThermopileSensor (Heimann Sensor GmbH). The HMS B21 Thermopile Sensor operatessimilar to the HMS Z11-F5.5 Ultrasmall Thermopile Sensor, describedpreviously, but has larger dimensions, i.e., 8.2 mm in diameter and 3 mmin height. The study showed that although the meter body had atemperature of approximately 30° C., the thermopile sensor was able tomeasure the temperature of an inserted test strip at room temperature,i.e. approximately 20° C. It is contemplated that other thermopilesensors may be used

In some embodiments, the temperature-measuring device 250 may also beemployed to measure temperature change that indicates the actualconcentration of an analyte. For instance, reaction between the analyteand the reagent may generate measurable heat that indicates theconcentration of the analyte in the sample.

In an alternative embodiment, the temperature-measuring system 250 mayinclude an optical-sensing system 250B as shown in FIG. 5. Rather thanmeasuring infrared radiation to calculate the temperature of the testsensor 100, the meter 200 may measure changes to temperature-sensitiveor thermochromic materials that are applied to the test sensor 100.Thermochromic materials change color according to changes intemperature.

In general, thermochromism is the reversible change in the spectralproperties of a substance that accompanies heating and cooling. Althoughthe actual meaning of the word specifies a visible color change,thermochromism may also include some cases for which the spectraltransition is either better observed outside of the visible region ornot observed in the visible at all. Thermochromism may occur in solid orliquid phase.

Light can interact with materials in the form of reflection, adsorptionor scattering, and temperature-dependent modifications of each of theselight-material interactions can lead to thermochromism. Thesethermochromic materials may include leuco dyes and cholesteric liquidcrystals. Other thermocromic materials also include electroactivepolymers, such as polyacetylenes, polythiophenes, or polyanilines.Classes of thermochromic materials are illustrated according to thephysical background in TABLE 1.

TABLE 1 Thermochromic Material Material feature Interaction Cholestericliquid crystals Periodic structure Reflection Crystalline colloidalarrays embedded in a gel network Inorganic salts Conjugated polymersChromophoric group Absorption Hydrogel-indicator dye systems Leucodye-developer-solvent systems Hydrogel exhibiting LCST Areas withdifferent Scattering refractive indices Polymer blends exhibiting LCST

Such temperature-sensitive materials may generally be applied on anyportion of the meter-contact area 112. In the embodiment of FIG. 1, athermochromic material may be applied to the auto-calibrationinformation area 120. Referring back to FIG. 5, a general configurationfor the optical-sensing system 250B is illustrated. The optical-sensingsystem 250B may include a light source 252B and a detector 254B. Thelight source 252B transmits photons from the thermchromic material, andthe detector 254B receives the photons that are reflected from thethennchromic material. For example, the light source 252B may be one ormore laser LEDs, while the detector 254B may be one or more photodiodes.For materials, such as ChromaZone (a microencapsulated thermochromicpigment) which changes from color to colorless as the temperatureincreases, and vice versa, the temperature can be determined bymeasuring the level of reflection from the material.

Although the optical-sensing system 250B may actually measure thetemperature of the test sensor 100, i.e. the meter-contact area 112,instead of the temperature of the reagent 115, the temperatures of thetest sensor 100 and the reagent 115 are generally at equilibrium withthe ambient temperature when the test sensor 100 when the test sensor100 is inserted into the test-sensor opening 210 at time t₁. Asdescribed previously, when the test sensor 100 is inserted into thetest-sensor opening 210, the meter-contact area 112 is positioned in thetest-sensor opening 210, but the fluid-receiving area 110 may bepositioned distally from the meter 200. As such, the meter-contact area112 may be heated by sources of heat in the meter 200, such ascomponents receiving power from a power source. However, thefluid-receiving area 110 and the reagent 115 may be sufficiently spacedfrom the sources of heat to remain substantially at ambient temperature.Thus, determining the ambient temperature provides a useful estimate ofthe temperature of the reagent 115, which is used as a factor indetermining analyte concentration. It has been determined that for ashort period time, e.g., approximately 0.5 seconds to approximately 5seconds, after the test sensor 100 has been inserted into thetest-sensor opening 210 at time t₁, the ambient temperature can still bedetermined from the meter-contact area 112 before the temperature of thearea 112 increases due to the heat from the meter 200 or decreases dueto the cooling from the meter 200. Accordingly, some embodiments of thepresent invention measure the temperature of area 112 at time t₁ whenthe effects of heat or cooling from the meter 200 are still at aminimum. As described previously, other embodiments may measure thetemperature at other times and account for the effects of heating orcooling from the meter 200 by applying an algorithm. Furthermore, asalso described previously, alternative embodiments may include more thanone structure disposed anywhere relative to the meter body 205 formeasuring more than one area of the test sensor 100 inside or theoutside test-sensor opening 210.

To further explain aspects of embodiments employing a thermochromicmaterial, thermochromic liquid crystals (TCLCs) are described in detail.Thin film TCLCs are commercially available. For example, FIG. 6illustrates a test sensor 100 that is configured to use a TCLC 130B. TheTCLC 130B is applied in an area 133B that is defined by a thin curedmaterial 132B, such as an epoxy resin, which is applied to a back layeror window 135B. A front window or substrate 134B is formed over the TCLC130B.

In some embodiments, an array of thermochromic materials correspondingto varying temperature ranges may be employed to measure thetemperatures. For example, FIG. 12 illustrates “a sliced-pie TCLCconfiguration” 300 including eight TCLC circular segments 310, eachbeing sensitive for a smaller temperature range. Eight miniature LEDs320 are sequentially employed, and a single miniaturized RGB 330 isplaced in the center to detects the corresponding color.

TCLCs may provide certain advantages over other thermochromic materials.For example, while leuco dyes may provide a wide range of colors, TCLCsmay respond more precisely and can be engineered for more accuracy thanleuco dyes. It is understood, however, that the examples provided hereinare provided for illustrative purposes only.

TCLCs are characterized by well analyzed reflections of the visiblelight within a certain bandwidth of temperature. Typically, TCLC's arespecified for their color play. The resulting color play is highlysensitive to changes in temperature. A certain temperature leads to acertain reflected wavelength spectrum, with a local maximum at a certainwavelength and a narrow bandwidth. Accordingly, the optical-sensingsystem 250B may employ a liquid crystal temperature sensor that can beoptimized to read a temperature range of approximately 5° C. to 40° C.,for example. In this example, the lower end of the range of 5° C. may bereferred to as the “Red Start” temperature, and the higher end of 40° C.may be referred to as the “Blue Start” temperature. The bandwidthbetween the Red Start and Blue Start temperatures is thus 35° C. It iscontemplated that Red and Blue Starts may vary from these examples.

When the temperature of the TCLC is below the Red Start temperature,TCLC, particularly when applied in thin layers, are optically inactiveor transparent. Below the start temperature of the color change, TCLCshydrodynamically behave like a high viscosity paste. They aretransparent when applied in thin layers, or milky-white in bulk. In thisinitial state, the molecules are still ordered and close to each otheras in a solid crystal, as shown in FIG. 7. As the temperature increasestoward the Red Start temperature, the molecules are separated intolayers as they pass through the Smectic phase, but in this Mesomorphicstate, the crystals are still optically inactive or transparent.

Above the Red Start temperature, the molecules are in the cholestericstate, where they are optically active and reflect the light selectivelyand strongly depending on temperature. With increasing temperature, thelight reflected from the thermochromic layer changes, in sequence, fromred to orange, to yellow, to green, and then to blue. The molecules arenow arranged in layers, within which the alignment is identical. Inbetween layers, however, the molecule orientation is twisted by acertain angle. The light passing the liquid crystal (LC) undergoes Braggdiffraction on these layers, and the wavelength with the greatestconstructive interference is reflected back, which is perceived as aspectral color. As the crystal undergoes changes in temperature, thermalexpansion occurs, resulting in change of spacing between the layers, andtherefore in the reflected wavelength. Specifically, cumulatively anoverall helix-shaped architecture is formed, and the molecular directortraces out a helix in space. The degree of twist is defined by the pitchlength L₀, which is the height of the helical structure after one 360°rotation. The angle between two layers and thereby the pitch length ofthe helix is proportional to the wavelength λ₀ of the selectivelyreflected light. This relationship can be described by the Braggdiffraction equation, where n_(mean) is the mean refraction index and φis the angle of the incident light beam with respect to the normal ofthe surface:

λ₀ =L ₀ ·n _(mean)·sin φ  (1)

If the temperature increases beyond the Blue Start temperature, themolecular structure of the helix disbands and the molecules areuniformly distributed like in an isotropic liquid. In this state, thecrystals are optically inactive again. Exceeding the Blue Starttemperature may lead to a permanent damage of the TCLCs, depending ontime and extent of the overheating.

The bandwidth of the TCLCs is defined as optical active range and islimited downward by a Red-start temperature and upward by a Blue-endtemperature. The light passing the liquid crystal undergoes Braggdiffraction on these layers, and the wavelength with the greatestconstructive interference is reflected back, which is perceived as aspectral color. As the crystal undergoes changes in temperature, thermalexpansion occurs, resulting in change of spacing between the layers, andtherefore in the reflected wavelength. The color of the thermochromicliquid crystal can therefore continuously range from black through thespectral colors to black again, depending on the temperature. as shownin FIG. 8.

As the TCLCs only have thermochromic properties when they are in theCholesteric state, a thermochromic material having a specifiedtemperature range can be engineered by mixing different cholestericcompounds.

To demonstrate the principle of some aspects of employing TCLCs, anexperiment was conducted. The first step included preparing somecholesteryl ester liquid crystals using a known method, based on G. H.Brown and J. J. Wolken, Liquid Crystals and Biological Systems, AcademicPress, NY, 1979, pp. 165-167 and W. Elser and R. D. Ennulat, Adv. Liq.Cryst. 2, 73 (1976), the contents of which are incorporated herein byreference. The start materials were: (A) Cholesteryl oleyl carbonate,(Aldrich 15,115-7), (B) Cholesteryl pelargonate (Cholesteryl nonanoate)(Aldrich C7,880-1), and (C) Cholesteryl benzoate (Aldrich C7,580-2).Different compositions of the mixture of these three chemicals A, B, andC producing a liquid crystal film change color over differenttemperature ranges as shown in TABLE 2.

TABLE 2 A = Cholesteryl B = Cholesteryl C = Cholesteryl Transition oleylCarbonate, g pelargonate, g benzoate, g range, ° C. 0.65 0.25 0.10 17-230.70 0.10 0.20 20-25 0.45 0.45 0.10 26.5-30.5 0.43 0.47 0.10 29-32 0.440.46 0.10 30-33 0.42 0.48 0.10 31-34 0.40 0.50 0.10 32-35 0.38 0.52 0.1033-36 0.36 0.54 0.10 34-37 0.34 0.56 0.10 35-38 0.32 0.58 0.10 36-390.30 0.60 0.10 37-40

These liquid crystals reversibly change color as the temperaturechanges. An advantage of liquid crystals is their ability to map outthermal regions of different temperature. The liquid crystal mixturechanges color with temperature. The TCLC film may degrade when exposedto moisture or air, but as long as they are stored in a sealed containerthe mixture may be prepared months in advance.

The example experimental setup in the demonstration included the TCLCfilms from Liquid Crystal Resources Inc (Glenview, Ill.), an opticalRed-Green-Blue (RGB) sensor and software TCS230EVM from Texas AdvancedOptoelectronic Solutions (Plano, Tex.), a programmable heating andcooling plate IC35 from Torrey Pines Scientific, Inc. (San Marcos,Calif.). Several K type thermocouples from Omega Engineering Inc,Stamford Conn. were used to ascertain the temperature on theheating-cooling plate. The TLC film was attached to the heater/coolerplate, and temperature was set at 5-45° C., in 5° C. steps. Threethermocouples were taped to the film and one to the plate. Two differentTLC films were used: 5-20° C. and 20-40° C. Both temperature and RGBdata were captured at a frequency of 20 Hz using DAQ.

The results of the example experimental setup above are described. Thetemperature vs. time and optical intensity vs. time data illustrated inFIG. 9 were converted to temperature vs. color intensity dataillustrated in FIG. 10.

FIG. 11A illustrates a subroutine for optical processing to convert RGBdata into temperature data. The optical data acquired is in athree-column format with r_(s), g_(s), b_(s) being the values for red,green and blue sample. The data is used to evaluate the ratios rg andrb. The ratios are then matched to the mapping file which has thecalibration data red, green, blue and temperature data r_(c), g_(c),b_(c) and T_(c). FIG. 11B illustrates a general algorithm to processoptical data to convert RGB data into temperature data.

Data for the 20° C. to 40° C. temperature tests are shown in FIG. 12. Asshown in FIG. 13, the temperature-time and color intensity-time data areconverted to temperature-color intensity data. The TCLC-basedtemperature are compared with thermocouple data in FIG. 15.

After applying the algorithms of FIGS. 11A and 11B, the temperaturescalculated from the RGB sensor follow the thermocouple data closely.Accordingly, the demonstration above shows that optical data can beconverted into temperature data and the use of optical data from TCLCfilm for temperature measurement is feasible. In general, a TCLC filmmay be used in conjunction with an RGB sensor for measuring the sensortemperature. The change in color of the film may be calibrated to atemperature of the strip. Furthermore, studies have shown that thetechnique of using a TCLC film works for varying temperature differencesbetween the sensor and the meter. In one aspect, the temperaturedifference may be approximately 45° C. In another aspect, thetemperature difference may be approximately 25° C. In yet anotheraspect, the temperature difference may be approximately 10° C.

To measure the color of the TCLC, in one embodiment, the optical-sensingsystem 250B may employ the general configuration shown in FIG. 5. Inparticular, the light source 252B may be three LEDs corresponding tored, green, and blue wavelengths, or may be a single LED emitting whitelight. Three separate photodiodes with filters measure the reflectionR_(r), R_(g), and R_(h) from the TCLC corresponding to red, green, andblue wavelengths, respectively. The ratio R_(r):R_(g):R_(b) changesaccording to color change in the TCLC. As the TCLC changes from red togreen to blue with increasing temperatures, the ratios R_(r):R_(b) andR_(r):R_(g) decrease with the increase in temperature. Thus, thetemperature of the TCLC may be determined from the ratioR_(r):R_(g):R_(b). Other ratios between R_(r), R_(g), and R_(b) may beemployed by other embodiments. In addition, a calibration feature may berequired for this embodiment.

In yet another embodiment, the optical-sensing system 250B may alsoemploy the general configuration shown in FIG. 5. However, the lightsource 252B may be a LED emitting a white light, while the detector 254Bmay be an integrated red/green/blue (RGB) color sensor detecting thelevel of red, green, and blue light reflecting from the TCLC. Theamounts of red, green, and blue light indicate the color and thus thetemperature of the TCLC.

In a further embodiment, the optical-sensing system 250B also employsthe general configuration shown in FIG. 5. In this embodiment, the lightsource 252B may be a LED emitting photons of a certain wavelength, whilethe detector 254B may be a photodiode measuring the reflection ofphotons of the certain wavelength. The amount of reflection changes asthe color of the TCLC changes. Thus, the measured reflection indicatesthe temperature of the TCLC.

Rather than using the general configuration of FIG. 5, theoptical-sensing system 250B in an alternative embodiment may employ anassembly that integrates illumination optics and receiver circuitry,including a red/green/blue (RGB) color sensor. This “hybrid” assembly,or combined structure, employs separate LED light sources to transmitred, green, and blue light to the TCLC. The reflected signal for eachcolor may then be measured and converted into 16-bit data, for example,to enable color recognition, and thus a temperature reading, by theprocessing system 230.

Referring to FIG. 16, another embodiment for a temperature-measuringsystem 250 is illustrated. In particular, the embodiment of FIG. 16employs an optical-sensing system 250C that includes a light source 252Cand a detector array 254C. The light source 252C may be a laser thatemits a high coherence of a fixed wavelength λ. (Alternatively, thelight source 252C may include a light-emitting diode (LED) and filtersto generate light, e.g., a narrow band light beam, of fixed wavelengthλ.) The wavelength λ, for example, may be in the visible range, e.g.,approximately 700 nm. However, the wavelength λ may generally be in therange of approximately 450 nm to approximately 1800 nm. Meanwhile, thedetector array 254C may include a linear photodiode array, e.g.,silicon- or germanium-based photodiode array, that is capable ofreceiving and detecting light at any location along the length of thearray. The detector array 254C generates a voltage or current signalthat communicates the location. where light has been detected.

In contrast to the optical-sensing system 250B of FIG. 5, which measureschanges to thermochromic materials applied to the test sensor 100, theoptical-sensing system 250C measures changes to the structure of agrating 130C disposed along the surface of the test sensor 100. Asdescribed in further detail below, the structure of the grating 130Cprovides an indicator for temperature. In particular, the grating 130Cincludes a series of parallel linear structures 131C, which are spacedequally at a fixed distance d. For example, the distance d may beapproximately 600 nm. However, the distance d may vary in relation tothe wavelength λ. On some typical test sensors, the grating 130C may besized approximately 1 mm×1 mm. In some embodiments, the grating 130C maybe formed directly on the test sensor 100, which may be made from apolymer, such as PET (polyethylene terephalate). For example, a seriesof equidistant parallel grooves may be rolled into the material of thetest sensor 100. In another example, laser processing may be employed toengrave a series of equidistant parallel grooves into the surface of thetest sensor 100. In other embodiments, the grating 130C may be formedfrom another material and placed or affixed onto the surface of the testsensor 100. For example, a material may be applied to the surface of thetest sensor 100 by deposition to provide a grating structure. Ingeneral, the grating 130C has substantially the same temperature of theunderlying test sensor 100.

As shown in FIG. 16, the light source 252C directs light of fixedwavelength λ toward the grating 130C at a given angle of incidence. Thegrating 130C causes diffraction of the light, and the diffracted lightis received by the detector array 254C. According to the diffractionequation:

m λ=d sin θ  (2),

where d is the distance between the linear structures 131C for thegrating 130C, λ is the wavelength of the incident light from lightsource 252C, θ is the angle at which the light is directed from thegrating 130C, and m is an integer representing each maxima for thediffracted light. For a given maxima in the diffraction pattern, lightof wavelength λ reflects at a specific angle θ off the grating 130C. Theoptical-sensing system 250C may be configured so that the detector 254Cdetects light corresponding to a given maxima, e.g., first order maximaat m=1. The angle θ from the grating 130C can be determined according tothe location where the detector array 254C receives the light from thegrating 130C. Thus, for a given wavelength λ, the angle θ measured withthe detector 254C indicates the distance d between the structures 131C.

The grating 130C is formed from a material that is sensitive totemperature. In general, the material expands when the temperature Tincreases, and the material contracts when the temperature T decreases.Correspondingly, the distance d between the linear structures 131Cchanges according to the temperature of the material. In other words,the distance d increases when the temperature T increases and decreaseswhen the temperature T decreases. The distance d is a function oftemperature, d(T), and from equation (2) above:

sin θ=m λ/d(T)  (3).

Thus, the angle θ is also a function of temperature and can be measuredwith the detector 254C to determine the temperature T of the gratingmaterial. Because the grating 130C is thermally coupled to the testsensor 100, the temperature T of the grating material also indicates thetemperature of the underlying test sensor 100. Preferably, the grating130C is formed from a material with a sufficiently high coefficient ofthermal expansion, so that the grating 130B has a highly detectablesensitivity to temperature and the temperature measurement can beachieved with greater accuracy. In addition, a more accuratedetermination of the angle θ may be achieved by positioning the detectorarray 254C at a greater distance from the grating 130C, although thepositioning of the detector array 254C may depend on how theoptical-sensing system 250C is assembled in the meter 200. Thecorrelation between the measured angle θ and the temperature T can bedetermined empirically for a given material and configuration of thegrating 130C. As a result, the optical-sensing system 250C illustratedin FIG. 16 may be employed to estimate the temperature of the reagentand, as described previously, to obtain a more accurate calculation ofthe concentration of analyte in a sample collected on the test sensor100.

Referring to FIG. 17, another embodiment for a temperature-measuringsystem 250 is illustrated. The embodiment of FIG. 17 employs anoptical-sensing system 250D that includes a light source 252D and adetector 254D. However, instead of providing a laser of a fixedwavelength λ, the light source 252D emits white light. In oneembodiment, the light source 252D may be an LED. Meanwhile, the detector254D may include an integrated red/green/blue (RGB) color sensor. Forexample, the detector 254D may include RGB photodiodes that provide avoltage or current signal that indicates the level of red, green, andblue components in the light received by the detector 254D.

A grating 130D similar to the grating 130D of FIG. 16 is disposed alongthe surface of the test sensor 100. The grating 130D includes a seriesof parallel linear structures 131D, which are equally spaced at a fixeddistance d. As described previously, the material forming the grating130D expands and contracts in response to the temperature.Correspondingly, the distance d increases and decreases when thematerial responds to the temperature.

As shown in FIG. 17, the light source 252D directs white light towardthe grating 130D. The grating 130D causes diffraction of the whitelight, and some of the diffracted light is received by the detector254D. According to the wavelength dependence shown in the gratingequation (2) above, the grating 130D separates the incident white lightinto its constituent wavelength components, and each wavelengthcomponent is emitted from the grating 130D at a particular angle θ. Thedetector 254D is not configured as an array that receives all wavelengthcomponents from the grating 130D. Thus, as shown in FIG. 17, thedetector 254D receives the diffracted light within a range of angles θ.The detector 254D detects the red, green, and blue components of thelight it receives. A RGB numerical value can be generated to representthe level of red, green, and blue components in the light received bythe detector 254D.

However, as described previously, the distance d between the linearstructures 131D changes when the temperature changes. The change indistance d also changes the diffraction of light from the grating 130D.In particular, the angle θ changes for each wavelength component in theincident white light. Moreover, the light received by the detector 254Dwithin the range of angles θ changes. With the change in the receivedlight, the red, green, and blue components measured by the detector 254Dalso changes. In other words, the light received by the detector 254Dexperiences a color shift when the temperature changes. For example, acolor shift that increases the level of blue in the received light mayindicate a decrease in temperature, while a color shift that increasesthe level of red in the received light may indicate an increase intemperature. Correspondingly, the RGB numerical value representing thelevel of red, green, and blue components in the received light alsochanges.

Accordingly, the color, i.e. the RGB numerical value, of the lightreceived by the detector 254D can be measured to determine thetemperature T of the grating material. Because the grating 130D isthermally coupled to the test sensor 100, the temperature T of thegrating material also indicates the temperature of the underlying testsensor 100. Preferably, the grating 130D is formed from a material witha sufficiently high coefficient of thermal expansion, so that thegrating 130D has a highly detectable sensitivity to temperature and thetemperature measurement is accurate. The correlation between the colorand the temperature T can be determined empirically for a given materialand configuration of the grating 130C. As a result, the optical-sensingsystem 250D illustrated in FIG. 17 may be employed to estimate thetemperature of the reagent and, as described previously, to obtain amore accurate calculation of the concentration of analyte in the samplecollected on the test sensor 100.

Referring to FIG. 18, yet another embodiment for a temperature-measuringsystem 250 is illustrated. The embodiment of FIG. 18 employs anoptical-sensing system 250E that includes a light source 252E and adetector 254E. The light source 252E may be a laser that emits a highcoherence of a fixed wavelength λ. (Alternatively, the light source 252Cmay include a light-emitting diode (LED) and filters to generate light,e.g., a narrow band light beam, of fixed wavelength λ.) Meanwhile, thedetector 254E may include a single photodiode that provides a current orvoltage signal indicating the amount of light received by thephotodiode. Rather than a grating, however, a polarizing material 130Eis disposed along the surface of the test sensor 100.

As shown in FIG. 18, the light source 252D directs the laser toward thepolarizing material 130E and light is reflected from the polarizingmaterial 130E to the detector 254E. The polarizing material 130E causesa change in the polarization of the light from the light source 252E. Asshown further in FIG. 18, a polarizing filter 255E is disposed betweenthe polarizing material 130E and the detector 254E, so that only lightthat is polarized in a particular direction passes to the detector 254E.Thus, the amount of light received by the detector 254E depends on thepolarization of the reflected light. However, the structure of thepolarizing material 130E and thus the degree of polarization of thereflected light depends on the temperature. Any change in the degree ofpolarization of the reflected light results in a change in the amount oflight received by the detector 254E. Thus, the amount of light thedetector 254D receives can be measured to determine the temperature T ofthe polarizing material 130E. Because the polarizing material 130E isthermally coupled to the test sensor 100, the temperature T of thepolarizing material 130E also indicates the temperature of theunderlying test sensor 100. The correlation between the amount of lightreceived by the detector 254E and the temperature T can be determinedempirically for a given polarizing material 130E. As a result, theoptical-sensing system 250E illustrated in FIG. 18 may be employed toestimate the temperature of the reagent and, as described previously, toobtain a more accurate calculation of the concentration of analyte inthe sample collected on the test sensor 100.

Although the embodiments described herein provide more accuratetemperature readings than conventional systems, it has been discoveredthat further accuracy may be achieved by optimal positioning of thesensor of the temperature-measuring system 250 within the test-sensoropening 210. For example, as shown in FIG. 3E, the thermopile sensor250A occupies a position 251 within the test-sensor opening 210. In someembodiments, this may mean that the sensor 250A is positioned near theelectrical contacts that receive the test sensor electrodes. When thethermopile sensor 250A is positioned more deeply within the interior ofthe meter 210 in the direction X shown FIG. 3E, the thermopile sensor250A measures the temperature at a region 113 of the meter-contact area112 where heat transfer from the meter 200 is minimized. In one aspect,convective heat transfer is reduced at positions deeper within thetest-sensor opening 210. Thus, the temperature at a region deeper withinthe test-sensor opening 210 changes more slowly, so that there is agreater chance of obtaining an accurate measurement of the temperatureof the test sensor 100 without the effects of heat transfer from themeter 200.

In the embodiments described herein, heat transfer to the measuredregion 113 on the test sensor 100 may also be minimized by providing aspace between the region 113 and the thermopile sensor 250A to create aninsulating air pocket around the region 113. In addition, conductiveheat transfer to the test sensor 100 may be reduced by employing pointcontacts, rather than surface contacts, where any contact between themeter 200 and the test sensor 100 is necessary.

In general, the meter 200 employs an architecture that combines ananalog front end with a digital engine. Typically, the analog front endrelates to components such as the measurement system 220. Meanwhile, thedigital engine executes data processing functions and controlselectronic components such as the user interface 240. It is contemplatedthat the architecture in the embodiments described herein can beconfigured so that the temperature-measuring system 250 may beintegrated with the analog front end or the digital engine.Advantageously, when the temperature-measuring system 250 is integratedwith the analog front end, fewer electronic components are required fordesigning and implementing the temperature-measuring system 250. On theother hand, when temperature-measuring system 250 is integrated with thedigital engine, the architecture enables different configurations for ananalog front end to be designed and implemented with the digital enginewithout having to design each front end configuration to handletemperature measurement functions.

Although the embodiments described herein may measure the temperature ofone or more areas of a test sensor to determine the temperature of areagent disposed on the test sensor, it is contemplated that thetemperature of the reagent may be measured directly according to thetechniques described. For example, a thermochromic material may beapplied at or near the reagent to measure the temperature of thereagent.

The temperature measurement techniques described herein may also be usedin a controller employed in combination with a continuous glucosemonitoring (CGM) system 400 as shown in FIG. 19. Typically in the CGMsystem 400, a CGM sensor 410 is attached to a user. The CGM sensor 410may be placed in contact or optical communication with the user's bloodor interstitial fluid to measure a desired analyte concentration in thesample. The CGM sensor 410 may measure a desired analyte concentrationof the user through the skin. Once the CGM sensor 410 has measured aanalyte concentration, i.e., glucose, as known to those in the art, asignal is sent to a controller 420 or similar device. The CGM system 400may take measurements at different time intervals. As illustrated, thecontroller 420 is remote from the CGM sensor 410 in FIG. 19, but inother embodiments, the controller 420 may be attached to the CGM sensor410. However, most CGM systems must be calibrated at different timeintervals such that the CGM system produces a more accurate value. Tocalibrate the CGM system 400, a discrete blood glucose meter, such asthe embodiments described above, may be used to provide an accuratereading at a given time frame. The reading can then be used to calibrateCGM system 400. The meter used for such a task may be a meter 200 orother meters described previously herein or the meter may simply be amodule 430 that is contained within controller 420. The controller 420provides similar functions as meter 200 and has like components asprevious embodiments discussed herein. The module 430 may be integralwith controller 420 or simply be a component part that is added into thecontroller. The module 430 has an opening 432 to receive a test sensorstrip, which may be similar to sensor 100 or other embodiments aspreviously described herein and can calculate the concentration ofglucose in a sample as earlier described with reference to previousembodiments. In an alternate embodiment, some of the software or otherelectrical components required to calculate the concentration of glucosein the sample may be contained on the controller 420 apart from themodule 430. In either case the module 430 may have a connector 434 thatelectrically or optically connects the module 430 to the controller 420.The controller may also have a display 440 so as to display the measuredglucose reading. The module 430, similar to previous embodiments mayinclude one or more temperature measuring systems 250. The temperaturemeasuring system 250 may employ the measurement techniques describedherein or may include aspects of the temperature measuring systemsdescribed herein. For example, the temperature measuring system 250 mayinclude a thermopile sensor or employ an optical-sensing system toprovide more accurate measurements that account for temperature effects.The components may be positioned or configured similarly as previouslydiscussed.

While various embodiments in accordance with the present invention havebeen shown and described, it is understood that the invention is notlimited thereto. The present invention may be changed, modified andfurther applied by those skilled in the art. Therefore, this inventionis not limited to the detail shown and described previously, but alsoincludes all such changes and modifications.

1-14. (canceled)
 15. A method for determining an analyte concentrationin a sample of body fluid, comprising the steps of: receiving a testsensor, the test sensor comprising a fluid-receiving area for receivinga sample of body fluid, the fluid-receiving area containing a reagentthat produces a measurable reaction with an analyte in the sample, thetest sensor having a test-sensor temperature and the reagent having areagent temperature, wherein the test sensor has a grating disposedalong a surface of the test sensor, the grating including a series ofparallel linear structures equally separated by a distance that changesin response to temperature; determining, with a temperature-measuringsystem, a measurement of the test-sensor temperature when the testsensor is received, wherein the temperature-measuring system includes alight source and a light detector, the light source being configured todirect incident light to the grating, and the detector being configuredto receive, from the grating, diffracted light that changes according tochanges in the distance separating the linear structures of the grating,the temperature-measuring system determining the measurement of thetest-sensor temperature according to the diffracted light; anddetermining a concentration of the analyte in the sample according tothe measurement of the reaction and the measurement of the test-sensortemperature.
 16. The method of claim 15, wherein the light sourceincludes a laser of a fixed wavelength directed to the grating, and thedetector receives the diffracted light from the grating according to anangle, the angle indicating the distance separating the linearstructures of the grating, and the temperature-measuring systemdetermining the measurement of the test-sensor temperature according tothe angle.
 17. The method of claim 16, wherein the fixed wavelengthranges from approximately 450 nm to 1800 nm.
 18. The method of claim 16,wherein the detector includes a linear photodiode array.
 19. The methodof claim 15, wherein the light source generates white light and directsthe white light to the grating, and the detector receives the diffractedlight from the grating, the diffracted light including red, green, andblue (RGB) components, the RGB components in the diffracted lightindicating the distance separating the linear structures of the grating,and the temperature-measuring system determining the measurement of thetest-sensor temperature according to the angle.
 20. The method of claim19, wherein the detector includes red, green, and blue photodiodes. 21.A method for determining an analyte concentration in a sample of bodyfluid, comprising the steps of: receiving a test sensor, the test sensorcomprising a fluid-receiving area for receiving a sample of body fluid,the fluid-receiving area containing a reagent that produces a measurablereaction with an analyte in the sample, the test sensor having atest-sensor temperature and the reagent having a reagent temperature,wherein the test sensor has a polarizing material disposed along asurface of the test sensor, the polarizing material causing a degree ofpolarization of light reflected from the polarizing material, thepolarizing material having a structure that changes in response totemperature and changes the degree of polarization; determining, with atemperature-measuring system, a measurement of the test-sensortemperature when the test sensor is received, wherein thetemperature-measuring system includes a light source and a lightdetector, the light source being configured to direct incident light tothe polarizing material, and the detector being configured to receive,from the polarizing material, an amount of reflected light that changesaccording to the degree of polarization, the temperature-measuringsystem determining the measurement of the test-sensor temperatureaccording to the amount of reflected light received by the detector; anddetermining a concentration of the analyte in the sample according tothe measurement of the reaction and the measurement of the test-sensortemperature.
 22. The method of claim 21, wherein the light sourceincludes a laser of a fixed wavelength directed to the polarizingmaterial.
 23. The method of claim 22, wherein the fixed wavelengthranges from approximately 450 nm to 1800 nm.
 24. The method of claim 21,wherein the detector includes photodiode and a polarizing filter.